The present invention relates to a semiconductor device and a method of manufacturing same.
As a power semiconductor device, for example, a trench gate type vertical MOSFET (metal oxide semiconductor field effect transistor) has conventionally been known.
When a noise occurs in such a trench gate type vertical MOSFET, the noise passes through a junction capacitance of a pn junction formed between its drift region and base region. A noise having a low frequency, however, increases the impedance of this junction capacitance. This causes the problem that the noise cannot easily pass through this junction capacitance.
As a semiconductor device capable of overcoming this problem, proposed are the semiconductor device described in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2009-260271) and the semiconductor device described in Patent Document 2 (U.S. Pat. No. 5,998,833).
The semiconductor substrate of the semiconductor device described in Patent Document 1 has a trench MOS region in which a trench type vertical MOSFET is to be formed and a capacitance formation region. In the capacitance formation region, the semiconductor substrate has a trench extending from the main surface to the back surface in the drift region, an insulating film formed on the surface of the trench, and a conductive film formed on an insulator film. The conductive film has a source potential. Therefore, the conductive film and the drift region have therebetween a source-drain capacitance.
The semiconductor device described in Patent Document 2 has, in the semiconductor substrate, a gate electrode insulated from and opposite to a portion of a base region sandwiched between a source region and a drift region and a conductive film insulated from and opposite to the drift region. The gate electrode and the conductive film are in a trench extending from the main surface of the semiconductor substrate to the back surface side thereof. The conductive film has a source potential and is placed on the side of the back surface relative to the gate electrode. A source-drain capacitance is therefore formed between the conductive film and the drift region.